The present invention relates to a solid golf ball having exceptional rebound characteristics and flight performance, as well as good shot feel.
Golf balls can be broadly classified into two types: solid golf balls, which exhibit exceptional durability and flight distance, and thread-wound golf balls, which exhibit exceptional controllability and shot feel. Solid golf balls comprise a two-piece golf ball, of which a core is covered by a cover material, and a multi-layer structured golf ball, in which one or more intermediate layers are interposed between the core and cover.
The core of the solid golf balls is formed by a vulcanized molded article of rubber composition. The rubber composition comprises polybutadiene as a base rubber, a metal salt of xcex1,xcex2-unsaturated carboxylic acid and an organic peroxide. The metal salt of xcex1,xcex2-unsaturated carboxylic acid is grafted onto the polybutadiene main chain through the action of the organic peroxide, which serves as a free radical initiator, and functions as a co-crosslinking agent in the rubber composition. Since the vulcanized molded article of the rubber composition forms the three-dimensionally crosslinked structure therein, it is known to impart the core with a suitable degree of hardness and durability, and solid golf balls, in which such cores are employed, with exceptional durability, as well as good rebound characteristics and flight performance.
However, in comparison with conventional thread-wound golf balls, such solid golf balls have very hard shot feel as well as poor controllability at approach shot. In order to improve the shot feel, there has been an attempt of softening the core by lowering its hardness. The shot feel is improved as a result, but the rebound characteristics are degraded, which does not allow a sufficient flight distance to be obtained. In order to improve the controllability, an attempt of softening the cover has been proposed (Japanese Patent Kokai Publication No. 51406/1995). Whereas the spin performance is improved, the rebound characteristics of the cover are degraded, which led to the problem of sufficient flight performance of the resulting golf ball not being obtained.
Other attempts to accomplish an improvement in both the rebound characteristics and shot feel of solid golf balls have been made by compounding conventional core rubber compositions with various organic sulfide compounds (Japanese Patent Kokai Publication No. 244019/1998, Japanese Patent No. 2778229 and Japanese Patent No. 2669051). However, these attempts have still not yielded a golf ball that is satisfactory from the standpoints of both rebound characteristics and shot feel.
Japanese Patent Kokai Publication No. 89750/1987 proposes that 100 parts by weight of a blend of
(A) a polybutadiene having a Mooney viscosity of 70 to 100 [ML1+4(100xc2x0 C.)], synthesized using nickel-containing catalyst and/or cobalt-containing catalyst, and
(B) less than 50 parts by weight of a polybutadiene having a Mooney viscosity of 30 to 90 [ML1+4(100xc2x0 C.)], synthesized using a catalyst consisting of lanthanide rare earth elements-containing compound, or
(C) from 20 to 80 parts by weight of a polybutadiene having a Mooney viscosity of 20 to 50 [ML1+4(100xc2x0 C.)], synthesized using nickel-containing catalyst and/or cobalt-containing catalyst can be suitably used as a rubber composition for golf balls. When the blend is used for the rubber composition, initial velocity of the resulting golf ball is improved. However, shot feel of the resulting golf ball is not described.
There has been no golf ball, which is sufficient to accomplish the balance between rebound characteristics and shot feel at the time of hitting. It has been required to provide golf balls, of which the shot feel and the flight performance are improved still more.
A main object of the present invention is to provide a solid golf ball having exceptional rebound characteristics and flight performance, as well as good shot feel.
According to the present invention, the object described above has been accomplished by employing polybutadiene rubber containing a cis-1,4-bond of not less than 99% as a base rubber, thereby providing a solid golf ball having exceptional rebound characteristics and flight performance, as well as good shot feel.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.